The ESTRO-QUALity assurance network (EQUAL)

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• The European Society for Radiotherapy and Oncology (ESTRO) established the Quality Assurance network (EQUAL) to assess external radiotherapy dose delivery.
• External audits utilize mailed thermoluminescent dosimeters (TLDs) for measurements under reference and non-reference conditions.

Purpose of the Study:

• To evaluate the accuracy of radiation dose delivery in external radiotherapy through a quality assurance program.
• To identify potential deviations in dose output, depth dose, and wedge transmission factors.

Main Methods:

• Thermoluminescent dosimeters (TLDs) made of LiF powder (DTL 937) were read using an automatic TLD reader (PCL 3).
• Participating centers delivered a calculated absorbed dose of 2 Gy to TLDs for up to three photon energies, with 10 on-axis points per beam.
• Key parameters assessed included reference beam output, output variation with collimator settings, depth dose data, and wedge transmission factors.

Main Results:

• In 1998, 102 centers and 235 beams (28 Co-60, 207 X-ray) were audited.
• Approximately 3% of reference beam outputs and percentage depth doses deviated beyond the +/-5% tolerance.
• Deviations of 6% were observed for beam output variation and wedge transmission factors, particularly for large/rectangular fields and wedged beams.

Conclusions:

• The EQUAL program underscores the critical role of quality assurance in radiotherapy, especially for non-reference points on the beam axis.
• Continuous monitoring and adherence to quality standards are essential for ensuring accurate and safe radiation therapy delivery.